<h2>Problem 187</h2>
<div style="color:#666;font-size:80%;">22 March 2008</div><br />
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<p>A composite is a number containing at least two prime factors. For example, 15 = 3 <img src='images/symbol_times.gif' width='9' height='9' alt='&times;' border='0' style='vertical-align:middle;' /> 5; 9 = 3 <img src='images/symbol_times.gif' width='9' height='9' alt='&times;' border='0' style='vertical-align:middle;' /> 3; 12 = 2 <img src='images/symbol_times.gif' width='9' height='9' alt='&times;' border='0' style='vertical-align:middle;' /> 2 <img src='images/symbol_times.gif' width='9' height='9' alt='&times;' border='0' style='vertical-align:middle;' /> 3.</p>

<p>There are ten composites below thirty containing precisely two, not necessarily distinct, prime factors:
4, 6, 9, 10, 14, 15, 21, 22, 25, 26.</p>

<p>How many composite integers, <var>n</var> <img src='images/symbol_lt.gif' width='10' height='10' alt='&lt;' border='0' style='vertical-align:middle;' /> 10<img src="" style="display:none;" alt="^(" /><sup>8</sup><img src="" style="display:none;" alt=")" />, have precisely two, not necessarily distinct, prime factors?</p>
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